[sdiy] really basic question .. tolerance

[patchell]

    Heres one for you to think about.  You have a 10K resistor with a +100ppm./C
tempco and a 100K resistor with a +1000ppm/C tempco, you connect them together in
parrallel to make ~9K, what is the tempco of the resulting ~9K resistance?

    Guess I should work this one out myself to see what the answer is...

    Just a brain teaser I thought up on the spur of the moment...

harrybissell wrote:

> Tell ya what John...
>
> I'll buy your arguement that it can't be worse than the original tolerance...
>
> if you buy mine that its likely to be BETTER than the original tolerance...
>
> H^) harry
>
> John L Marshall wrote:
>
> > Tim or Harry or Peter,
> >
> > Please show me an example of two 1% resistors in series or parallel where
> > the tolerance exceeds 1%. I heard this rule many times but I can't see it.
> >
> > Complex circuits are another story. I can see how errors accumulate through
> > gain stages.
> >
> > I need empirical evidence to be convinced.
> >
> > Take care,
> > John
> > www.sound-photo.com
> > ---------------------------------------------------------------------------
> >
> > ----- Original Message -----
> > From: "Tim Ressel" <madhun2001 at yahoo.com>
> > To: "diysynth" <diy_list at analog-synth.de>; <synth-diy at dropmix.xs4all.nl>
> > Sent: Saturday, January 18, 2003 1:32 PM
> > Subject: Re: [sdiy] really basic question .. tolerance
> >
> > > Joerg,
> > >
> > > That is an optimistic way of looking at it. However
> > > the worse-case is still the sum. If I'm worrying about
> > > tolerances, I always look at worse-case.
> > >
> > > --tim
> > >
> > >
> > >
> > > --- diysynth <diy_list at analog-synth.de> wrote:
> > > > Hi all
> > > >
> > > > > tolerance are connected in series that the result
> > > > will be out of
> > > > tolerance?
> > > > >
> > > > > Add two 100k resistors 101k + 101k = 202k still 1%
> > > >
> > > > Sure ? I allways thought, the resulting tolerance
> > > > gets better with the
> > > > factor t_res=t_single/sqrt(n), where n is the number
> > > > of used resistors, and
> > > > t_single is the tolerance of the single resistor ?
> > > >
> > > > Joerg
> > > >
> > > >
> > >
> > >
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--
 -Jim
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